IDTechEx’ insight on touch technologies for flexible displays: Page 2 of 3

June 20, 2019 //By Julien Happich
flexible displays
The technologies seeking to unseat ITO (Indium Tin Oxide) are by now themselves old, at least in the sense that they have been around for a decade and a half, but they now have to compete on flexibility and foldability too if they are to be successful in flexible displays.

Combining the touch with other layer functionalities may partially alleviate this shortcoming. This trend towards combinations will accelerate perhaps with wide availability of CPI films. Candidates for function combination include the hard coat layer, the polarizer, the barrier film (if film is used), and so on. The evolution of this trend can have important implications for the long-term viability of film-based solutions.

In the comparative table, ‘low’ means lower than the other, the same applies to ‘high’. Another key parameter is the ability to sustain ever tightening foldability requirements. A thinner solution will offer higher foldability but this may need to be balanced by mechanical robustness and lifetime.

The other approach is on-cell. Here, the touch layers are deposited and photolithographically patterned inline directly on top of the OLED-TFT stack. In the future, it might be possible to weave the patterned touch electrodes as part of the TFT structure, although that can require a difficult manufacturing challenge.

The key advantage of this approach is that it eliminates the additional substrate, thus resulting in a thin and flexible solution. The challenge, however, is that it dramatically increases the cost of production defects in the touch layer as the entire stack- including the OLED and the TFT- will be thrown away.

Success here, therefore, requires outstanding production know-how and optimization. Furthermore, this process ties up more expensive production assets on a usually low-cost item which is the touch layer. It is also likely to require slow and controlled deposition within the narrow parameter space limited by the already-deposited materials and layers. Importantly, it is not clear whether this approach can be readily scaled to larger areas or not. This is because one would require the inline TFE as well as the patterned touch electrode deposition processes to be scaled up without compromising quality or cost.

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